Various combined door locks and alarms have heretofore been devised for sounding an alarm in response to an attempt to open a lock with an improper key. Illustrative in this regard is U.S. Pat. No. 2,563,727 to Kempf. Such devices have not gained any appreciable acceptance for use in ordinary residences because of their expense. Further such devices have typically required highly unusual keys for which blanks are not readily available making it difficult to obtain duplicate keys.